Sunday, January 31, 2016

It was a big day for the Biomarkers & Milk group. We had
an important paper accepted at Annals of Human Biology. This paper is the
second paper to come out of the Milk with Altitude Project (2013 edition), and
I assure you, there will be more!

This paper is important to me because it is further evidence
for a hypothesis I have been working on. As I have written before, as an
anthropologist, I tend to study non-western populations, and my research is
primarily concentrated with two groups: Filipinos living in Cebu, Philippines,
and ethnic Tibetans living in Nepal. Recently, working with an outstanding
team of undergraduates, we published a paper looking at the hormone adiponectin
in milk samples from 113 Filipino women.

So why are we excited about this? In the Cebu adiponectin
article, we reported something new and different about milk adiponectin and
child growth. Prior to our work, a phenomenal piece by Woo et al., (2012) had
shown a significant, inverse association between milk adiponectin and infant
weight for age z-score. Simply put: more adiponectin in milk, less growth in
the child. BUT – and here’s the cool part – they found that the slower growing
children had faster growth from 1-2 years of age.

Katie Hinde over at Mammals Suck suggested that this may be
an adaptive strategy to allow mothers to mediate their energetic investment in
offspring. By down regulating growth while it is directly dependent on her
metabolism, mothers may be able to conceive sooner. The catch-up growth from
1-2 years then, makes complete sense – children are then growing when other
community members can contribute to their energetic budgets.

And we think we’ve found the corollary – such trade-offs are
environmentally sensitive. In a high resource (low pathogen?) environment such
as that of the mothers Woo et al., studied, this is an excellent reproductive
strategy, as it allows mothers to defer some of the costs of reproduction to
others. However, in a low resource (high pathogen?) environment, the resources
necessary to support later growth may be unavailable, and it may be a better
reproductive strategy to promote early growth – when maternal metabolism can
support it.

For the Cebu study, we had mean adiponectin levels of 7
ng/mL of milk, compared to 21 ng/mL for the US women Woo et al., studied. Child
weight for age (centiles) also differed – the 50th percentile for
our sample was equivalent to the 5th percentile for US infants. However,
when we used a similar analytical technique as Woo et al., a really interesting
picture emerged (Figure 1). Our data fit almost perfectly with that of Woo et
al. In their model, there is a plateau for the association between milk
adiponectin and child growth at lower levels of milk adiponectin (10-13 ng/mL)
followed by a decline in weight for age as milk adiponectin increases. We found
a positive association between milk adiponectin and infant weight for age at
even lower levels of milk adiponectin (2 ng/mL to 8 ng/mL) – however there was
a plateauing of the association from about 8-10 ng/mL, or the max of our range.
The distribution of milk adiponectin in our sample barely overlapped with that
of Woo et al.

Figure 1: Comparison of weight-for-age percentiles by milk adiponectin between the Woo et al., study and the Cebu study. C

When you put the two datasets together, instead of forming alternative models, they form a complementary model suggesting that the
association between milk adiponectin and child weight for age z-score is not a
linear association but rather a bell-shaped association, where at a very low
levels (<7ng/mL) milk adiponectin is positively associated with growth, a
flattening of the association at levels of 7-12 ng/mL (intermediate levels) and
then an inverse association between milk adiponectin and growth at higher
(>12 ng/mL) levels. And because milk adiponectin had not generally been
studied in non-Western populations, such association was largely missed. This
is why studying milk composition in a diversity of human populations and
ecological zones is so important.

We’ve replicated this in our Tibetan study, but that’s a
separate post because the relationships get even more interesting. Once the Tibetan
study is out, I’ll continue the discussion started here with that piece.

Saturday, January 2, 2016

I have not been very reliable about posting to this blog.
Part of that was that 2015 was an unbelievably busy year for me, and I had very
little time for the blog. Another part of the issue was me - I was uncertain as
to whether or not this was still a priority for me. In 2015, I received a large
grant from the National Science Foundation for a 3 year birth cohort study in
Nubri, Nepal. This project is HUGE and has been very time consuming. I have
backed off on the blog simply to have more time for this project.

So what is the future of Biomarkers&Milk? I’m staying. I’m
committing to 12 posts in 2016 – one a month – plus additional topical posts.

Growing up with altitude: field report

Last month, I arrived back in the United States after a
month long field season in the Himalayas. As it is mid-semester, my trip was
designed to maximize field time and minimize missed classroom time. I missed
six classes, generous covered by my colleagues from within and outside of the
university. We spent just over 3 weeks in the field, and one week in Kathmandu.
I arrived Friday evening and we left Sunday afternoon for Nubri; we returned to
Kathmandu on Monday and left Friday for the United States. In the interim, we
had an amazingly successful project – in 3 weeks, we measured from than 500
children living in the Nubri Valley in 11 major villages and 5 smaller villages
both on and off the tourist routes. Upon returning to Kathmandu, we made
arrangements with the two largest boarding schools to come and measure children
from Nubri who were currently in Kathmandu for schooling. We measured another
270 children in Kathmandu over a 4 day period, bringing our total to just under
800. Based on our demographic data and population census data from the Nepali
government, we captured more than 80% of Nubri children, with all but about 35
children living in the Nubri valley measured. We had 1 refusal, and missed the
rest of the children because of comings and goings to and from the boarding
schools within the villages – they would be in their home village when we
measured the boarding school and then in the boarding school when we reached
the home village. We also measured almost all women of reproductive age in the
villages.

Figure 2: A village in Nubri.

What can I say about the growth project? It was exhausting,
and we collected an unbelievable amount of data in just a few weeks. I just
started entering data, and it will be a long, but steady process to get
everything worked out. We saw unbelievable patterns of migration, and many of
the biological and social processes going on will require considerable
investigation and thought before we are able – and willing – to better share
the research. The growth project was generously sponsored by an early career
development grant from the American Association of Physical Anthropologists.

Figure 3: My three AMAZING field assistants and I. This photo was taken by our camp manager.

The primary reason we were in Nubri however, was to start a
longitudinal birth cohort. Thanks to a substantial grant by the National
Science Foundation, we have funds to start the first ever high altitude birth
cohort study. Over the next 18 months, all children born in 11 study villages
will be recruited into the birth cohort. We had intended on recruiting from 9
study villages; my field assistants who will be living in Nubri for the next
several years, insisted that we add in three extra villages and remove one
village from the study. I think they had great justifications for this, and we
have modified recruitment accordingly. We also happened to have great luck with
births, and were around for six births, which meant I was able to get birth
weights almost immediately. Another 20 women were 5-9 months pregnant and
agreed to be in the study – meaning we are starting the birth cohort off with
26 mothers – about a quarter of our targeted sample size. Infants in the birth
cohort will be measured at birth by community midwives and each month
thereafter until 1 year of age by the 3 field assistants living in the Nubri
Valley. We’ll collect milk, basic anthropometrics on mothers and infants,
health histories, feeding histories, caregiving and breastfeeding practices,
and some really cool body composition data. It is a huge, exhaustive project
but has incredible potential to transform what we know about infancy and early
childhood in high altitude adapted – and high altitude living – populations.